1. Field of the Invention
The present invention relates to a prism sheet employed in a backlight module.
2. Description of the Related Art
Referring to FIGS. 9 and 10, a typical direct type backlight module 100 includes a frame 11, a plurality of light sources 12, a light diffusion plate 13, and a typical prism sheet 10. The light sources 12 are positioned in an inner side of the frame 11. The light diffusion plate 13 and the typical prism sheet 10 are positioned on the light sources 12 above a top of the frame 11. The light diffusion plate 13 includes a plurality of diffusing particles (not shown) configured for diffusing light. The typical prism sheet 10 includes a transparent substrate 101 and a prism layer 103 formed on a surface of the transparent substrate 101. A plurality of elongated V-shaped ridges 105 is formed on the prism layer 103.
In use, light emitted from the light sources 12 enters the diffusion plate 13 and becomes scattered. The scattered light leaves the diffusion plate 13, travels through the typical prism sheet 10, and is refracted out at the elongated V-shaped ridges 105.
The refracted light leaving the typical prism sheet 10 is concentrated at the prism layer 103 and increases the brightness of the prism sheet 10. The refracted light propagates into a liquid crystal display panel (not shown) positioned above the prism sheet 10.
However, although light from the light sources 12 enters the diffusion plate 13 and becomes scattered, the light leaves the prism sheet 10, and forms strong light spots.
In order to reduce or eliminate the strong light spots, the backlight module 100 should further include an upper light diffusion film 14 disposed on the typical prism sheet 10.
However, although the upper light diffusion film 14 and the typical prism sheet 10 are contacting each other, a plurality of air pockets exist around the boundaries of the light diffusion film 14 and the typical prism sheet 10. When light passes through the air pockets, some of the light undergoes total reflection along one or another of the corresponding boundaries. In addition, the upper light diffusion film 14 may absorb a certain amount of the light from the prism sheet 10. As a result, a brightness of light illumination of the backlight module 100 is reduced.
Therefore, a new prism sheet is desired to overcome the above-described shortcomings.